1) Field of the Invention
This invention relates generally to fabrication of semiconductor devices and more particularly to the formation of spacers on gate structures for self aligned contact (SAC) structures for CMOS semiconductor devices.
2) Description of the Prior Art
The self aligned contact (SAC) is a powerful method used in semiconductor manufacturing to reduce chip size by shortening the separation of contact to polysilicon. This is especially true in memory products. The space used for lightly doped drain (LDD) limits the smallest size possible with SAC. Creation of a double spacer helps alleviate the conflict between LDD and SAC requirements.
U.S. Pat. No. 5,923,986(Shen) (same inventor as present invention) shows a method for a double spacer (1 full and 1 partial top spacer) for a Self aligned silicide (SALICIDE) process. This process differs from the process of the present invention that is directed to a distinctly different process/structure--a self aligned contact (SAC).
In U.S. Pat. No. 5,208,472 (Su et al.) a method of forming a SAC structure is described where a first side wall is used to define a LDD structure, and a second side wall is used to extend the oxide region at the gate edge and improve source/drain leakage property.
In U.S. Pat. No. 4,912,061 (Nasr) a method is described for fabricating a self aligned metal oxide semiconductor device using a disposable silicon nitride spacer.
U.S. Pat. No. 5,651,857(Cronin et al.) shows a top half spacer.
U.S. Pat. No. 5,879,993(Chien et al.) shows a double spacer (1 full and 1 half bottom spacer) for a contact structure.
U.S. Pat. No. 5,663,586(Lin) shows a double spacers process.
The use of spacers are important in forming SAC structures and protecting LDD near a gate which can lead to higher densities and smaller chips; however, there is a limit to which the density can be increased, particularly when the LDD and SAC requirements are in conflict. It is, therefore, the purpose of this invention to teach a means by which spacers can be used without the conflicting requirements of the lightly doped drain and the self aligned contact. It is also a purpose of the invention to teach a means that the gate structure can be protected by a top spacer etch buffer so that the SAC opening etch will not create shorts to the gate structure.